1. Field of the Invention
The present invention is directed to printheads, specifically to a printhead having a pressure relief mechanism initiated by the approach of a radio frequency identification (RFID) circuit located on or within the print media.
2. Description of the Related Art
JP 11138941 describes a thermal printer system in which a mechanical sensor is used to detect the presence of a high spot in print media. When the mechanical sensor detects a high spot a head lifting mechanism is activated which moves the printhead to a non-contact position, off of the surface of the print media.
This design is susceptible to premature wear and failure due to repeated mechanical cycling of the sensor between up and down positions and use of a roller and spring. The roller and spring mechanism being susceptible to fowling from stray fibers and other contaminants associated with print media. When a high point is detected, the printhead is completely removed from contact with the print media, removing the ability for printing upon the raised section of print media. The mechanical head lifting mechanism is not adjustable to compensate for use of thicker or thinner overall print media. If too thick a print media is used, it is possible that the sensor will be permanently raised, preventing operation of the printer.
RFID tags typically range between 10-20 mils in thickness. Conventional thermo-printers are capable of printing upon print media with a thickness in the range of 3-12 mils. As an RFID circuit embedded in print media passes a printhead the printhead pressure at the contact point can theoretically increase by as much as six times. Abnormal pressure at the printhead contact point causes premature wear due to increased abrasion and creates an increased opportunity for over heating of the print media against the printhead heater elements. If an even pressure is maintained between the printhead and print medium, continuous printing is enabled and printhead life is extended.